1. Field of the Invention
The invention pertains to a bridge circuit comprising a plurality of field-effect power transistors for driving a brushless DC motor and in particular a drive circuit for driving said power transistors as a bridge circuit for driving a brushless DC motor having a plurality of n-channel field-effect transistors (FETs) which are fed by one single DC voltage source.
2. Description of the Prior Art
It is desirable to provide a simple drive circuit which facilitates a safe driving of power transistors connected to the positive line of a supply voltage without requiring the utilization of an additional voltage source in form of a DC-DC transformer or p-channel transistors.
It is also very desirable for cost reasons to construct a bridge circuit consisting of field-effect transistors exclusively with n-channel transistors since p-channel transistors with identical capacity are in accordance with the current state of the art substantially larger and more expensive than n-channel transistors. However, there exists the specific problem that the transistors connected to the positive line of the supply voltage require a gate potential in order to be switched on, with said gate potential lying substantially above the potential of the positive line of the supply voltage and thus not easily available. The obvious solution of generating this auxiliary potential by means of a DC-DC voltage transformer or a battery is not very advantageous for cost reasons.